1. Field of the Invention
The present invention relates to a semiconductor device using a crystalline semiconductor film crystallized by radiating an amorphous semiconductor film with a laser beam and a method of manufacturing the same.
2. Description of the Related Art
There has been a known technology for crystallizing an amorphous semiconductor film formed on a substrate such as glass by means of a laser process. The laser process means a method of recrystallizing a damaged or amorphous film formed on a semiconductor substrate or a semiconductor film, a method of crystallizing an amorphous semiconductor film formed on an insulating surface or a method of improving crystallinity of a semiconductor film (crystalline semiconductor film) having a crystalline structure. A gas laser represented by an excimer laser or a solid laser represented by a YGA laser is usually used as a laser oscillator device used for the laser process.
A feature of using a laser beam is in that a laser beam is used for radiation and an area absorbing an energy of the laser beam can only be heated selectively, different from a case of a heating process using radiating heating or conducting heating. For example, in a laser process using an excimer laser oscillator device, a process of crystallization or activation of a semiconductor film is achieved by heating a semiconductor film selectively and locally with almost no heat-damage to a glass substrate.
As an example of the laser process, there is a known method of processing a beam linearly by means of an optical system to use the beam for radiation like a laser processing device disclosed in Japanese Patent Laid-Open No. 8-195357. Further, a method of crystallization with a solid laser oscillator device such as an Nd:YVO4 laser is disclosed in Japanese Patent Laid-Open No. 2001-144027. This document discloses that the second higher harmonic of a laser beam used for radiation from the solid laser oscillator device allows the crystalline semiconductor film to have a larger grain size than conventional cases.
Especially, application to a thin film transistor (hereinafter referred to as a TFT) in a method of crystallization using a continuous wave solid laser oscillator device is reported in “Ultra-high Performance Poly-Si TFTs on a Glass by a Stable Scanning CW laser Lateral Crystallization”, A. Hara, F. Takeuchi, M. Takei, K. Yoshino, K. Suga and N. Sasaki, AMLCD '01 Tech. Dig., 2001, pp.227-230. This document discloses an example of a method of producing a TFT with a polycrystalline silicon film crystallized by means of the second higher harmonic of a solid continuous oscillator laser (YVO4) for diode excitation.